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Strange pump cycling problem


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Any help gratefully received ;

I have a, fairly new, Whale Watermaster 1214 running my water system. For no good reason, I decided to go for 4bar

Over the last few months, it's started cycling, every few minutes a quick burst. I put this down to an suspect old tap. I've checked every accessible junctions for leaks. When I was tracking it before I put a valve in the cold feed to the hot water system and that made no difference (other than that the expansion vessel is in this feed so it 'clicked' a little, often)  seeming to support my belief of the kitchen tap.

The last few days  it's got worse so I decided to investigate. The tap seems fine, no dampness. This time I put a valve in the cold feed one joint away from the pump and it still happens. Strangely when I turn off the water at the tanks (before the pump) but leave the pump switched on it doesn't happen.

Any ideas?

 

 

Edited by hounddog
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3 minutes ago, hounddog said:

Any help gratefully received ;

I have a, fairly new, Whale Watermaster 1214 running my water system. For no good reason, I decided to go for 4psi.

Over the last few months, it's started cycling, every few minutes a quick burst. I put this down to an suspect old tap. I've checked every accessible junctions for leaks. When I was tracking it before I put a valve in the cold feed to the hot water system and that made no difference (other than that the expansion vessel is in this feed so it 'clicked' a little, often)  seeming to support my belief of the kitchen tap.

The last few days  it's got worse so I decided to investigate. The tap seems fine, no dampness. This time I put a valve in the cold feed one joint away from the pump and it still happens. Strangely when I turn off the water at the tanks (before the pump) but leave the pump switched on it doesn't happen.

Any ideas?

 

 

Pressure relief valve on calorifier or back flow through the pump? 

Edited by rusty69
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1 minute ago, rusty69 said:

Pressure relief valve on calorifier? 

Nope. Happens with the hot feed isolated (no difference in frequency)

As I say, the very strange thing is that if I turn off the feed to the pump (i.e. there's no pressure on the inlet) it doesn't happen.

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Back flow through the pump delivery valves. Once you shut the inlet valve from the tank there is nowhere for the backflow to go so it doesn't happen.

Theoretically!, if you fill the water tank the rate of cycling will reduce because the greater inlet head will slow the backflow.  I expect any difference will be hard to measure accurately though.

N

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6 minutes ago, BEngo said:

Back flow through the pump delivery valves. Once you shut the inlet valve from the tank there is nowhere for the backflow to go so it doesn't happen.

Theoretically!, if you fill the water tank the rate of cycling will reduce because the greater inlet head will slow the backflow.  I expect any difference will be hard to measure accurately though.

N

Assuming the op meant he had set the pump pressure to 4bar (not 4 psi) then that is equivalent to about 130 feet of water, so I agree that a few inches more or less in the tank will be very hard to measure any change in the backflow.

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11 minutes ago, BEngo said:

Back flow through the pump delivery valves. Once you shut the inlet valve from the tank there is nowhere for the backflow to go so it doesn't happen.

Theoretically!, if you fill the water tank the rate of cycling will reduce because the greater inlet head will slow the backflow.  I expect any difference will be hard to measure accurately though.

N

Would a non-return valve before the pump stop this? 

And yes, 4 bar, not 4 psi, thanks!

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5 minutes ago, hounddog said:

Would a non-return valve before the pump stop this? 

And yes, 4 bar, not 4 psi, thanks!

It should. But if it's a fairly new pump it shouldn't leak. Also what is your calorifier PRV rating? I thought they were usually 3bar.

Edited by rusty69
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In theory, yes provided it is close to the pump inlet.  In practice much will depend on the nrv.  If it needs much pressure across it to seal well then it will probably have no effect.

You could try running the pump with all taps open to see if you can flush out any micro dirt that is causing the leak back through the pump.

It should not be the PRV because it stops when you shut the tank off.  The PRV would not see that.

 

N

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It is not clear to me if you have an accumulator or not.  I know some modern pumps say they do not need one, but without you don't need much back flow for the pressure to drop.  Though they are not cheap, an accumulator - assuming you don't have one - would be the way to go.

Following on from the comment above, I think my calorifier came with a 3.5 or 4 bar prv - so if this is very close to pump pressure it may be weeping a bit.  Again if you don't have an accumulator if will not take much for the pump to start again, however as you said preventing the backflow by shutting the supply valve fixed it it is probably not this - though it might become a problem if the pump cut off pressure drifts up a bit over time - mine has, it was about 1.4Bar when new and is now about 1.6 bar.

 

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3 minutes ago, Chewbacka said:

It is not clear to me if you have an accumulator or not.  I know some modern pumps say they do not need one, but without you don't need much back flow for the pressure to drop.  Though they are not cheap, an accumulator - assuming you don't have one - would be the way to go.

Following on from the comment above, I think my calorifier came with a 3.5 or 4 bar prv - so if this is very close to pump pressure it may be weeping a bit.  Again if you don't have an accumulator if will not take much for the pump to start again, however as you said preventing the backflow by shutting the supply valve fixed it it is probably not this - though it might become a problem if the pump cut off pressure drifts up a bit over time - mine has, it was about 1.4Bar when new and is now about 1.6 bar.

 

I don't have an accumulator, the calorifier is tilted so has a air pocket and seems to work although I am planning to fit a proper accumulator at some time. 

The PRV is 3 Bar and the pump is, in fact 30psi, sorry! I can be useless with numbers sometimes 

I think Bengo has nailed it. I'm sat here now with the inlet shut off and it hasn't gone off at all.  

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27 minutes ago, hounddog said:

I don't have an accumulator, the calorifier is tilted so has a air pocket and seems to work although I am planning to fit a proper accumulator at some time. 

The PRV is 3 Bar and the pump is, in fact 30psi, sorry! I can be useless with numbers sometimes 

I think Bengo has nailed it. I'm sat here now with the inlet shut off and it hasn't gone off at all.  

As said, a NRV might work but it depends on how good it is and how much crud you have in the tank because a tiny bit getting stuck in the NRV could prevent it from completely closing. 

An accumulator might prove a better way forward. 

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Do you have an NRV between the hot and cold systems?  if so then the air pocket will act more as an expansion vessel and a hot side accumulator, but will have little effect on the cold system, so will do little to help with maintaining cold side pressure. 

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Just now, hounddog said:

Will that help the problem?  

Absolutely. As the water leaks back through the pump the accumulator will maintain the pressure in the system so that the pump's pressure switch doesn't switch on. 

Depending on the speed of the leak-back and the size of the accumulator it might not eliminate the cycling entirely but it should massively lengthen the time between cycles. 

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1 minute ago, hounddog said:

OK, thanks, it was on the list anyway as the air in the calorifier method seems a bit random

Plus, as Chewy pointed out, it won't work at all if you have an NRV on the calorifier input (which is usual). 

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1 hour ago, smileypete said:

Having some sort of valve on the outlet of the pump can save a bit of sanity troubleshooting....

indeed. It's tempting to put valves in everywhere there's a branch.

4 hours ago, Tony Brooks said:

FWIW - I would fit a plumbers flap type non-return valve between the strainer (you do have on on the pump feed I trust) and the pump. I have found this often "solves" this type of thing.

This is the next stage. Also dismantle the pump and strainer. The system kept pressure for about an hour with the inlet shut off. 

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The Wonderful Whale came back to me with a confirmation of the 'dirt in the valves' diagnosis;

Quote

If there is leak back in the head of the pump it is generally due to dirt caught below the inlet and outlet valves.
There is a service kit available to fix this issue, AK1316 universal replacement head.
I have attached a data sheet with an exploded view of the pump and service kits available.

If the issue is down to dirt it may be a good idea to replace the filter also.

 

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Unless you can guarantee that the PRV (f you have one) and the plumbing are not leaking I do not see how Whale can confirm its definitely dirt in a valve. All anyone can say is that there is a leak somewhere. Its a different matter if you are sure about plumbing leaks and the PRV.

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38 minutes ago, Tony Brooks said:

Unless you can guarantee that the PRV (f you have one) and the plumbing are not leaking I do not see how Whale can confirm its definitely dirt in a valve. All anyone can say is that there is a leak somewhere. Its a different matter if you are sure about plumbing leaks and the PRV.

Fully agree, but given the symptoms the op has reported, if you were Whale what could be 'wrong' with your pump given that the pump cycles frequently, but if the pump inlet valve is closed it does not cycle?  I can only assume it is backflow through the pump, which would indicate problems with the pump's internal valve.  Whale also started with "If there is leak back in the head of the pump...." therefore relying on the op's diagnosis of cause.

Edited by Chewbacka
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3 hours ago, Tony Brooks said:

Unless you can guarantee that the PRV (f you have one) and the plumbing are not leaking I do not see how Whale can confirm its definitely dirt in a valve. All anyone can say is that there is a leak somewhere. Its a different matter if you are sure about plumbing leaks and the PRV.

I opened this thread because I isolated the rest of the water system and the cycling still occurred.

I did this because I had examined the whole system and there is no water leak anywhere. 

I am willing to accept Bengo's and Whale's diagnosis. 

Edited by hounddog
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